Shock-produced high-pressure (La, Ce, Th)PO<inf>4</inf> polymorph revealed by microstructural phase heritage of monazite
MetadataShow full item record
The responses of uranium-bearing accessory minerals to shock metamorphism have received growing interest, because under extreme pressure and temperature conditions, these phases can form unique microstructures and/or polymorphs and their radiometric ages can be partially to wholly reset. This study presents new, high-resolution electron backscatter diffraction microstructural analyses of shock-deformed monazite, (La, Ce, Th)PO4, from the Haughton Dome, Nunavut, Canada, and the Nördlinger-Ries Crater, southern Germany. At each locality, shocked monazite grains contain distinctive lamellae comprising interlocking laths in four systematic crystallographic orientations. Modelling of orientation relationships among these lath-textured microstructures reveals that they were produced by reversion from lamellae of a previously undescribed high-pressure polymorph with a tetragonal symmetry. This is the first report of polymorphism found in natural (La, Ce, Th)PO4. The orientation relationships, lamellar forms, and ready reversion to monazite at low pressures are consistent with a deviatoric transformation. The former presence of this new (La, Ce, Th)PO4 polymorph is detected in moderately to highly shocked rocks, suggesting that it may be common at other impact craters.
Showing items related by title, author, creator and subject.
Nanoscale deformation twinning in xenotime, a new shocked mineral, from the Santa Fe impact structure (New Mexico, USA)Cavosie, Aaron; Montalvo, P.; Timms, Nicholas; Reddy, Steven (2016)Shock microstructures in refractory accessory minerals such as zircon and monazite provide crucial evidence for deciphering impact-related deformation in a wide variety of planetary materials. Here we describe the first ...
Deformation microstructures in zircon and monazite: implications for shock, tectonic and geochronological studiesErickson, Timmons Manning (2016)Zircon and monazite have been studied by quantitative microstructural analysis to constrain deformation processes in both tectonic and shock environments. Results provide new constraints on twinning, shock transformation ...
Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact agesErickson, T.; Timms, Nicholas Eric; Kirkland, Chris; Tohver, E.; Cavosie, Aaron; Pearce, M.; Reddy, Steven (2017)Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U–Th–Pb systematics ...